Ovarian carcinoma remains the cancer with the highest mortality rate among gynecological tumors. Although many ovarian cancer patients fully respond to the standard combination of surgery and chemotherapy, nearly 90% later develop recurrent chemotherapy-resistant cancer and inevitably succumb to their disease. Thus, development of innovative, effective therapies against recurrent/chemotherapy-resistant ovarian cancer remains a high priority for improving public health. Using high-throughput technologies to analyze genetic fingerprints of ovarian cancer, we have recently discovered extremely high expression of the genes encoding the proteins claudin-3 and claudin-4. Because claudin-3 and -4 are the epithelial receptors for Clostridium perfringens enterotoxin (CPE) and are sufficient to mediate CPE binding, which triggers subsequent toxin-mediated cytolysis, we hypothesize that using CPE to target ovarian cancer cells based on their high levels of claudin-3 and -4 is potentially a novel, highly effective therapeutic approach for chemotherapy-resistant ovarian cancer. Consistent with this view, we introduced CPE to cells cultured from several primary, metastatic, and chemotherapy-resistant ovarian cancers that overexpress claudin-3 and -4, and we found that these tumor cells, unlike healthy human tissues, are highly sensitive to CPE-mediated cytolysis. More importantly, we found that intraperitoneal CPE therapy in SCID mouse xenografts harboring a highly relevant clinical model of chemotherapy-resistant human ovarian cancer inhibited tumor growth in 100% of mice harboring 1-week established disease. Thus, using CPE to target the high levels of claudin-3 and -4 may represent an innovative, potentially highly effective therapeutic approach to kill metastatic and/or chemotherapy-resistant ovarian cancer cells. Accordingly, this proposal has three related specific aims: 1) Characterize profiles and regulation of expression of claudin-3 and -4 in ovarian cancer;2) Characterize sensitivity and resistance of ovarian cancer cells to CPE-mediated cytolysis;and 3) Examine in vivo the pharmacokinetics, efficacy, and toxicity of CPE therapy. Upon completion of this project, we will be positioned to quickly translate this research into a novel clinical treatment for patients with chemotherapy-resistant disease. Ovarian carcinoma remains the most lethal of gynecologic malignancies, with up to 90% of patients diagnosed with advanced stage ovarian cancer dying from recurrent chemotherapy-resistant tumors;therefore, development of novel therapies for this disease is a high priority for improving public health. Results of the proposed research will lay the foundation for rapid clinical translation of an innovative, potentially highly effective treatment for patients with chemotherapy-resistant ovarian cancer.